Hollow "wood"-type golf club heads are now in wide-spread use, and typically are fabricated of a thin hollow shell to which is attached a club shaft. These types of clubs have largely replaced the true wood clubs actually fabricated from persimmon wood, and are used as drivers and fairway "woods." The shell is typically a metal such as stainless steel, aluminum or titanium alloy, but other materials also include graphite, ceramics, polycarbonates and plastics.
A problem associated with hollow wood-type clubs is the vibration generated from impact with the ball. In some cases, the hollow shell may be filled with a foam urethane, which tends to provide some vibration dampening. However, over time and as the result of play with the club, the foam may degrade, and become detached from the interior surface of the head, thereby causing annoying rattles and sounds.